Require accepting ToS when enabling zeta (#23255)

Note: Design hasn't been reviewed yet, but the logic is done

When the user switches the inline completion provider to `zed`, we'll
show a modal prompting them to accept terms if they haven't done so:


https://github.com/user-attachments/assets/3fc6d368-c00a-4dcb-9484-fbbbb5eb859e

If they dismiss the modal, they'll be able to get to it again from the
inline completion button:


https://github.com/user-attachments/assets/cf842778-5538-4e06-9ed8-21579981cc47

This also stops zeta sending requests that will fail immediately when
ToS are not accepted.

Release Notes:

- N/A

---------

Co-authored-by: Richard <richard@zed.dev>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
Co-authored-by: Joao <joao@zed.dev>

crates/zed/src/main.rs

@@ -438,7 +438,11 @@ fn main() {
             cx,
         );
         snippet_provider::init(cx);
-        inline_completion_registry::init(app_state.client.clone(), cx);
+        inline_completion_registry::init(
+            app_state.client.clone(),
+            app_state.user_store.clone(),
+            cx,
+        );
         let prompt_builder = assistant::init(
             app_state.fs.clone(),
             app_state.client.clone(),